Most methods for detecting misfires require for detection the signals of special sensors such as those sensors which measure ignition currents, measure the pressure or light in the combustion chamber or detect knocking signals. However, one generally strives to utilize as few sensors as possible. A sensor which is perforce present on every modern engine control is one which measures the crankshaft angle. It is therefore desirable to utilize signals from this sensor for as many purposes as possible and even for detecting misfires.
Published German patent application 3,615,547 discloses a method wherein the signals of the crankshaft sensor are used for detecting misfires. In this method, the crankshaft speed is measured toward the end of the compression angular segment for each cylinder and near the end of the following expansion angular segment. When misfires occur, the difference between the two detected speeds is considerably less than for a correctly operating engine. Accordingly, misfires are detected with the aid of the measured values for which the measured values must still be corrected for engine speed effects and averaged.